Accretion definition, an increase by natural growth or by gradual external addition; growth in size or extent. See more.
Alveoli are tiny sacs within our lungs that allow oxygen and carbon dioxide to move between the lungs and bloodstream. Learn more about how they function and quiz your knowledge at the end.
An alveolus (plural: alveoli) is a word used in anatomy for hollow cavities, which are empty areas within a body. Although there are many different types of alveoli in the body, the word alveoli is usually used to talk about small air sacs in the lungs of mammals. These are also called pulmonary alveoli.These alveoli are located at the ends of the air passageways in the lungs.he concentration of carbon dioxide is lower in the alveolus than in the red blood cells, so carbon dioxide leaves the red blood cells, enters the alveolus, and is exhaled. In an average human lung, there are 480 million alveoli.